// VerifyTransaction checks that the inputs to the transaction exist,
// that the transaction does not create or destroy coins and that the
// signatures on the transaction are valid
func (bc Blockchain) VerifyTransaction(tx coin.Transaction) error {
//CHECKLIST: DONE: check for duplicate ux inputs/double spending
//CHECKLIST: DONE: check that inputs of transaction have not been spent
//CHECKLIST: DONE: check there are no duplicate outputs
// Q: why are coin hours based on last block time and not
// current time?
// A: no two computers will agree on system time. Need system clock
// indepedent timing that everyone agrees on. fee values would depend on
// local clock
// Check transaction type and length
// Check for duplicate outputs
// Check for duplicate inputs
// Check for invalid hash
// Check for no inputs
// Check for no outputs
// Check for non 1e6 multiple coin outputs
// Check for zero coin outputs
// Check valid looking signatures
if err := tx.Verify(); err != nil {
return err
}
uxIn, err := bc.unspent.GetMultiple(tx.In)
if err != nil {
return err
}
// Checks whether ux inputs exist,
// Check that signatures are allowed to spend inputs
if err := tx.VerifyInput(uxIn); err != nil {
return err
}
// Get the UxOuts we expect to have when the block is created.
uxOut := coin.CreateUnspents(bc.Head().Head, tx)
// Check that there are any duplicates within this set
if uxOut.HasDupes() {
return errors.New("Duplicate unspent outputs in transaction")
}
if DebugLevel1 {
// Check that new unspents don't collide with existing. This should
// also be checked in verifyTransactions
for i := range uxOut {
if bc.unspent.Has(uxOut[i].Hash()) {
return errors.New("New unspent collides with existing unspent")
}
}
}
// Check that no coins are lost, and sufficient coins and hours are spent
err = coin.VerifyTransactionSpending(bc.Time(), uxIn, uxOut)
if err != nil {
return err
}
return nil
}
func TestVerifyTransactionSpending(t *testing.T) {
ft := FakeTree{}
bc := NewBlockchain(&ft, nil)
bc.CreateGenesisBlock(genAddress, _genCoins, _genTime)
// Overspending hours
tx := coin.Transaction{}
uxs := bc.GetUnspent().Array()
tx.PushInput(uxs[0].Hash())
tx.PushOutput(genAddress, 1e6, uxs[0].Body.Hours)
tx.PushOutput(genAddress, uxs[0].Body.Coins-1e6, 1)
uxIn, err := bc.GetUnspent().GetMultiple(tx.In)
assert.Nil(t, err)
uxOut := coin.CreateUnspents(bc.Head().Head, tx)
assertError(t, coin.VerifyTransactionSpending(bc.Time(), uxIn, uxOut),
"Insufficient coin hours")
// add block to blockchain.
_, ux := addBlockToBlockchain(t, bc)
// addBlockToBlockchain(t, bc)
// Valid
tx, _ = makeTransactionForChainWithHoursFee(t, bc, ux, genSecret, 100, 50)
uxIn, err = bc.GetUnspent().GetMultiple(tx.In)
assert.Nil(t, err)
uxOut = coin.CreateUnspents(bc.Head().Head, tx)
assert.Nil(t, coin.VerifyTransactionSpending(bc.Time(), uxIn, uxOut))
// Destroying coins
tx = coin.Transaction{}
tx.PushInput(ux.Hash())
tx.PushOutput(genAddress, 1e6, 100)
tx.PushOutput(genAddress, 10e6, 100)
uxIn, err = bc.GetUnspent().GetMultiple(tx.In)
assert.Nil(t, err)
uxOut = coin.CreateUnspents(bc.Head().Head, tx)
err = coin.VerifyTransactionSpending(bc.Time(), uxIn, uxOut)
assert.NotNil(t, err)
assert.Equal(t, err.Error(),
"Transactions may not create or destroy coins")
assertError(t, coin.VerifyTransactionSpending(bc.Time(), uxIn, uxOut),
"Transactions may not create or destroy coins")
// Insufficient coins
tx = coin.Transaction{}
tx.PushInput(ux.Hash())
p, s := cipher.GenerateKeyPair()
a := cipher.AddressFromPubKey(p)
coins := ux.Body.Coins
assert.True(t, coins > 1e6)
tx.PushOutput(a, 1e6, 100)
tx.PushOutput(genAddress, coins-1e6, 100)
tx.SignInputs([]cipher.SecKey{genSecret})
tx.UpdateHeader()
b, err := bc.NewBlockFromTransactions(coin.Transactions{tx}, bc.Time()+_incTime)
assert.Nil(t, err)
uxs, err = bc.ExecuteBlock(&b)
assert.Nil(t, err)
tx = coin.Transaction{}
tx.PushInput(uxs[0].Hash())
tx.PushOutput(a, 10e6, 1)
tx.SignInputs([]cipher.SecKey{s})
tx.UpdateHeader()
uxIn, err = bc.GetUnspent().GetMultiple(tx.In)
assert.Nil(t, err)
uxOut = coin.CreateUnspents(bc.Head().Head, tx)
assertError(t, coin.VerifyTransactionSpending(bc.Time(), uxIn, uxOut),
"Insufficient coins")
}